A full, five-dimensional (5D) light field describes every possible view, from every possible angle, within the bounds of the region characterized by the light field. That is, the 5D light field, which is also known as the 5D plenoptic function, is a measure of the radiance as a function of three spatial coordinates, x, y, and z, and two angular coordinates, φ and θ. The radiance of rays propagating in empty regions remains constant, however, so one dimension of a 5D light field associated with an empty region contains redundant information. As a result, the light field describing an empty region can be characterized completely by measuring just four dimensions, which can be obtained in parallel planes.
4D light fields can be constructed from 2D images acquired at different planes with a conventional camera. For the 4D light field to be constructed precisely, however, the camera must be positioned precisely and/or its position must be precisely calibrated to the position of the light field's source. Although high-precision stages can be used to position the camera precisely, stages are bulky, move slowly, and draw large amounts of power. Moving the camera, then calibrating its position, also tends to be slow and may require additional equipment. Thus, conventional cameras are not suitable for measuring 4D light fields associated with moving objects.
Alternatively, 4D light fields can be constructed from multiple 2D images acquired in parallel from different angles or positions. For example, simultaneously capturing 2D images of a moving object with an array of cameras yields enough data to reconstruct the corresponding 4D light field. Camera arrays tend to be bulky, however, so they are not suitable for applications where small size is important, such as consumer photography.
Plenoptic cameras also capture multiple 2D images in parallel with a microlens array situated at the focal plane of a bulk lens. Each microlens images the aperture of the bulk lens onto a 2D detector array, which has multiple detector elements per microlens. Processing the array of images produced by the microlenses and captured by the detector array yields the 4D light field associated with the scene viewed by the bulk lens. Although plenoptic cameras can be quite compact, their resolution is much lower than the resolution of conventional cameras or camera arrays because they use just a few detector elements per microlens. For instance, using a 2000×2000 element detector array to capture images from 10,000 microlenses leaves only 400 detector elements per image. In addition, the microlenses must be aligned very precisely to the bulk lens and the detector array. Further, a plenoptic camera cannot be used to take conventional pictures.